Polymerase Beta Variants and Cancer. Abstract: DNA polymerase beta functions in base excision repair (BER) which is important for the repair of endogenous DNA damage and damage caused by agents such as ionizing radiation. The broad long-term objective of the proposed research is to understand how aberrant BER is linked to carcinogenesis and the treatment of cancer with agents including ionizing radiation. The application consists of three specific aims. The first aim is to test the hypothesis that a cancer-associated variant of Pol beta induces tumorigenesis in mice. The second aim is to test the hypothesis that a germline variant of Pol beta is linked to cancer. For these aims we will characterize spontaneous and induced tumorigenesis and mutagenesis. We have recently identified colon tumor variants of Pol beta and the third aim is to test the hypothesis that these variants are linked to cancer. We will employ the focus formation and anchorage independent growth assays to characterize cellular transformation. Genomic instability will be assessed using the cII and chromosomal aberration assays. The significance of these studies lies in understanding the role of BER as a tumor suppressor mechanism.